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Geothermal

Geothermal energy is heat generated and stored in the ground. New Zealand has an abundant supply of geothermal energy because we’re located on the boundary between two tectonic plates. This means that the Earth’s crust is thinner and the hot mantle below is much closer to the surface. Centuries before we began turning geothermal energy into electricity, Māori were cooking, washing and warming themselves with heat directly from the earth’s core. These days geothermal energy provides 22% of NZ’s total primary energy supply, including over 17% of our electricity.

How geothermal energy works

Geothermal power stations pipe geothermal fluid (a mixture of high pressure water and steam) from wells several kilometres deep to a central generation plant. The geothermal fluid is turned into steam that drives turbine generators to produce electricity. Used geothermal fluid is re-injected into wells to maintain pressure and structure, or in the case of older plants discharged into rivers. New Zealand also uses hot water and steam directly for industrial processes (particularly wood processing and paper-making) and to heat greenhouses and hot pools.

Pros and cons of geothermal energy

Geothermal energy supply doesn’t depend on weather conditions, making it consistent and reliable. It’s a renewable resource, but it needs careful management and monitoring to control water and pressure levels and prevent land subsidence and depletion.

Geothermal fluids also contain gases and minerals, though amounts vary from field to field, and the amount released depends on the design of power station. So electricity generated from geothermal energy does produce some greenhouse gas emissions. However, a geothermal power station still produces fewer greenhouse gas emissions than the cleanest natural gas-fuelled power station.

The future of geothermal energy

Total geothermal electricity capacity in New Zealand stands at over 900 MW. It has been estimated that there is approximately another 1,000 MW of geothermal resource that could be used for generating electricity.

We could also use more geothermal energy directly, for example as industrial process heat, or by finding uses for waste heat from geothermal power stations.